Because of the temporary nature of the installation of such antennas, to facilitate moving them it is known to assemble these masts from a plurality of generally cylindrical elements which, when they are installed, are joined end to end. At each of their end to end junctions, the elements are assembled by the engagement of one of the elements with a sleeve carried by the other element.
For a mast of this kind, the topmost elements supporting the antenna are first assembled. Then this group of elements is made to engage a vertical shaft which is supported on the ground via a base or supporting framework. To raise the antenna to the desired height, supplementary elements are passed upward through the bottom of this shaft to engage the lowermost element of the group and are themselves engaged in succession one to the other. The top of the mast is thereby raised progressively.
Naturally, to disassemble the mast this procedure is reversed.
The mast may be of a single pole type comprising a plurality of stacked elements or a lattice mast of the type described in aforenoted application Ser. No. 745,940.
The top of the mast is generally raised by the height of one element at a time. To effect this progressive elevation, a raising device is used that principally comprises a support plate which supports the element to be added to the group of elements supporting the antenna, the support plate is connected via a tieline to at least one raising device that enables the plate to be raised toward the bottom of the shaft, i.e. in the upward direction.
Typically, these raising devices comprise winches that are actuated by the operator or operators assembling the mast. A winch raising device typically includes a mechanism having a drum for winding up the tieline. The drum is driven in rotation by a device that reduces the effort to be exerted on the tieline. Naturally the mechanism also includes a suitable ratchet device by which untimely unwinding of the tieline on the drum can be prevented, due to the influence of the load being raised.
prior art raising mechanisms designed in this way give good results, especially in the case where heavy loads are raised. Nevertheless, they have the disadvantage of being bulky and relatively costly, taking into account their complexity and may require the availability of electrical power which is not readily available at remote field installations.